What does it mean "hierhin"?

What does it mean "hierhin"?
The complete sentense is "Wir haben gestern gut hierhin gefunden",I get the meaning "We found our way here all right yesterday".
But why do we put "hin" behind "hier"?Is it a preposition?When do we have to put one?(I'm a beginner)

Your guess is correct,"hin" is a preposition and indicates direction away from the speaker; it means to,towards,there:
simple question:Wohin gehen wir?= where do we go to?
sie sind gerade hineingekommen = they just came in there;arrived there/to that place
Ich fahre mit dem Auto hin = I go by car there
I falle hin = I fall down
hinlegen = lie down
alles deutet darauf hin = everything points to it
there is also |"her" which indicates just the opposite of "hin",the diraction towards the speaker,as in:hin und her = to and from; here and there
Imperative with "her":komm her!= come over here!
*Hin- and her-.Prepositional adverbs of motion are usually based on hin-,implying motion or direction away from the speaker,and her-,implying motion or direction towards the speaker.Hin and her are themselves stand-alone adverbs meaning the same thing,and describe less-specific motion or direction.(One example in which hin is an integral separable prefix is the verb hinrichten,which means "to execute.) Not all verbs formed from hin- and her- compounds are lexical.Some examples of hin- and her- compounds are:
herab (down,down from) hinein (in,inside) hinaus (out,out of,onto) darüber hinaus (furthermore,above all) dahin (in the direction/towards of known location)
Mastery of hin- and her- requires considerable effort from the student.
Da- compounds are also adverbs,corresponding to "there-" compounds in English.They replace specific prepositional objects.Although are used principally in legal texts and therefore sound formal in English,they are often employed in written and spoken German and are convenient replacements for long and complicated prepositional phrases.Their comprehension and active use are essential in German.Da- compounds are formed by adding da- before the preposition,with an "r" inserted before prepositions starting with a vowel.There are exceptions to this,and da- compounds are given a fuller treatment in the chapter on prepositions.
Hier- and dort- compounds also exist in German,though they are used less frequently.As in English,they are considered formal,and are used primarily in academic and legal texts.They are best memorized as vocabulary.
hierhin und dorthin - hither and thither
here are some good web-resources for you to practice German,check out: